Stabilized photographic silver halide emulsions



or during development STABILIZED .PHOTIOGRAPHICxSILY-ER EMULSIONS Charles F. H. Allen and John J. Sagura, Rochester, N.

assignors to Eastman Kodak Company, Rochester, N. Y., acorporationofN'ew Jersey No Drawing. Application January 1,6, 1956 Serial No. 552,097

9 Claims. (01.96-109) This invention relates to fog-inhibiting agents and sta-*- bilizers for photographic emulsions, and to photographic em l i s containing th m- It is well known that photographic emulsions .on storagetend. to lose sensitivity .and to become spontaneously developable without exposure to light. Thereis normally a detectable amount of thesilver salt reducedduring de velopment in the areas where noexposure was-"given; this; is commonly called fog, and sometimes called chemical :fog? where it is necessary to distinguish be tween it and the efiects of. accidental exposure to" radi"ation; in thisinvention, we are not "concerned with the latter.

Fog depends both on the emulsion :and the conditions of development; for a'given emulsion it increases with the. degree of development. Withconstant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stabilityofph otographic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur rump ical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to somev extent, against such eflects, it is normally understood that an antif oggantprotects against spontaneous growth of fog during prolonged storage or storage at high temperatures, and humidities, o ma mu con a n p e or both.

It is, accordingly, vide a method for stabilizing photographic emulsions. A further object of our invention is to maintain the sensitivity and fog of silver halide emulsions atlor close to initial optimum. values under keeping conditions of high temperature and humidity. A further ,Qbject is to prous hbt s aph sil er ha i e emulsions cont inin a t ifq san 9 s a i s,- Q h obi e s i l use ana snt rom a. easide ,t on o t e ew usde tiption'an xamples-i The above objects are accomplished by adding to the an object of our invention to prov i added in suitable 2 photographic emulsion a compound selected from those represented by the following general forrnulaz 1 (I) wherein R represents an alkoxylgroup, such as methoxyl, ethoxy l, etc. onanamino group and R represents a rhydrogen atom .or.,a lower alkyl gpoup, suehas methyl, ethyl, etc.

The fog inhibitors which we propose to use are added to the emulsion duringf t-he-process of manufacture, to avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of stor- A solution of thecompounds of the insventiori when concentration, befoi'e coatihg"," to 'unsensitized, chemically sensitized, or optically sensitized ph tographic emulsions does not appregiably .afiect the sensitometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are madeat, appreciable intervals of time, at elevated temperatures and, dry or somewhat humid conditions, these compounds do stabilize photographic speed and maintain fogat a low level.

Iheprepamtion of silver halide; emuls ons involves three separate operations: ,(lythe; emulsifi'eation. and digestionior ripening of the: silver halide, 62.) the? freeing of the emulsion from excesssojluble salts, usually "by ticing our invention. Thesecompounds belong to a group of compounds which we shall designate aslaminothiazoles. (,U 0

H=cn0ge.---N,

mul i-s11 S fi-amino-4-carh thoxy itnnereaptothiazdll a HsGaO-ii-GN' H e-( i- Lee ('33: S ii rnethylamino-4-narbetho;y-2-mereaptothiazole (3) 5 amlno-i-earbamyw-mercaptothiszole 5-ruethylamlno4 carburnethoxy-2-mercnptothiazole The above compounds can be prepared according to the methods of Cook et al., "Jour. Chem. Soc. (London), 1947, p. 1598, 1949, pps. 1064, 1441. 2329. The compounds of 'Formula I can, alternatively be written in the following form:

while the compounds of Formula 1 wherein R, is a methyl.

group can be written in the tautomcric term;

It is to be understood that our invention contemplates the-above compounds in any of their tautomericforms. An improved method for making compound 1 follows;

' Example'A. 5-amin0-4-carbethoxy-Z-mercaptothiazole 42, 735 (1909)) in 300 ml. of absolute ethanol was.

shaken for a few minutes with a teaspoon of Raney nickel. This treatment is necessary to remove materials which poison the platinum oxide catalyst. The mixture was then filtered and the filtrate was hydrogenated over 0.5 g. of platinum oxide catalyst at room temperature and under 2-3 atmospheres pressure of hydrogen for 22 to 24 hours. The catalyst was removed by filtration and the ethanolic solution of ethyl aminocyanoacetate (pure ethyl aminocyanoacetate prepared as a pale yellow liquid, 3.. P. 88-90 C. (1 mm.); n 1.4425) was boiled under reflux for one hour with '50 ml. of carbon disulfide. The resulting solution was concentrated in vacuo on the steam bath until crystallization occurred. The vacuum was then relieved and sufficient absolute ethanol was added to the boiling suspension to effect solution. The solution was clarified with charcoal and allowed to cool. The crystalline product was collected and recrystallized from absolute ethanol to afford 25 g. of white, granular crystals, M. P.'186-'187 C.

The photographic emulsions used in practicing our invention are generally of-the developing-out type; also, it is to be understood that photographic emulsions of varying halide content can advantageously be used.

The antifoggant compounds used in our invention have been found particularly useful when employed in conjunction with gelatino-silver bromiodide emulsions, although they can also be advantageously employed for stabilizing other silver halide emulsions, such as gelatinosilver chloride, bromide, chlorobromide, chlorobromiodide, etc.

' tion Serial No. 319,611 (now issued December 27, 1955), Carroll and Murray U. S.

of emulsions with respect to sensitivity,

- soluble salts (Lowe and Jones The emulsions can also be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U. S. Patent 1,574,944 and U. S. 1,623,499, and Sheppard and Brigham U. S. Patent 2,410,689.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium. iridium and platinum, all of which belong to group VIII of the periodic table of elements and have an atomic weight greater than 100. Representative compounds are ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U. S. Patent 2,448,060, and as antifoggants in higher amounts, as described in Trivelli and Smith U. S. Patents 2,566,245 and 2.566.263.

The emulsions can also be chemically sensitized with gold salts as described in Waller and Dodd U. S. Patent 2.399.083, or stabilized with gold salts as described in Damschroder U. S. Patent 2,597,856 and Yutzy and .amines such as spermine (Lowe and Allen U. S. Patent 2,521,925), or bis-(p-aminoethyl) sulfide and its water- U. S. Patent 2,521,926).

The emulsions can also be stabilized with the mercury compounds'of Allen, Byers and Murray U. S. applica- U. S. Patent No. 2,728,663,

application Serial No. 319,612 (now U. S. Patent No. 2,728,664, issued December 27, 1955) and Leubner and Murray U. S. application Serial No. 319,613 (now U. S.

-, Patent No. 2,728,665, issued December 27, 1955),all

filed November 8, 1952.

The stabilizing combinations of aminothiazoles are effective in the presence or absence of optical sensitiz.

ing dyes. Since optical sensitizing may aifect stability fog and latent image change s,, the action of the compounds of this .invention is not completely independent of optical sensitizing or other emulsion variables. We have found,

however, that both unsensitized emulsions and emulsions sensitized with cyanine orv merocyanine dyes or bothcan ,be treated with aminothiazoles according to our invention.

The antifoggant and stabilizing action was determined by incubation of the emulsions for the times indicated in the following table at a temperature of 120 F. and constant relative humidity (obtained by placing the emulsions in closed containers, the ambient temperature being about F. and relative humidity about 55 percent prior to scaling the containers) The efficiency'of the various antifoggants was determined by measuring the speed, gamma and fog of the incubated emulsions containing an antifoggant and comparing these measurements with those of the same batch of emulsion before incubation. Also similar measurements were-madeon a photographic emulsion containing no antifoggant,'both before and after incubation.

The tests were made using high speed silver bromiodide emulsions (coated on cellulose acetate supports), WhlCh had been panchromatically sensitized. The emulsions were exposedin an Eastman Type Ib sensitometer and developed, for the times indicated in the table, using the developers indicated. The spee'd,-gamma and fog for the emulsions were then measured as indicated above.

While the same batch of emulsion was not employed in colloids, such "all of the cramples, tl1e' sarne gbatch' wasemploy'ed in the coatings of each individual example for purposesof comparison.

-The optini m w; amount of "fog-inhibting. agent can "be determined by 'makihg the customary -test's employed in Fresh Test Incubation Test Developer Cone, Exam 1e Oom ound .mol i p N t gX Time I 1 .Tlme .Speed Gamma Fog (Wits) v Speed, ,Qarnma ,Fog .No. M nn)- u es 2,700 .72 .11 1 1,190 .67 .26 A i 6.5 2.950 .75 .11 1 B500 073 ;..20 A a 6.5 2,700 .72 .11 1 1, 190 67 .26 .A 10.5 .600 .71 .11 1 1,440 .65 :19 A r 6.5 2,250 .70 .09 2 ""1865 :60 .128 A 5 6.5 2.100 .65 .08 2 1,040 .58 .17 A 6.5 1 3,100 1. 23 .10 2 2,300 1.04 .22 B 4 3.150 1.24 .09 2 2.050 1.04 .17 B 4 8,050 1:04 .12 1 6.000 .96 21 7.200 .98 .11 1 6.400 .95 .12 C 5 7.900 1.00 .12 1 6.150 97 .16 O 5 7, 900 99 12 1 6, 250 96 010 C 5 In the above tableydeveloper A had the following composition:

Water to make 1 liter.

As shown in the above Cook et al. references, the compounds of Formula I above wherein R is an alkyl group can be prepared by simply intermixing an alkaline solution of a compound of Formula I wherein R is a hydrogen atom with an alkyl salt, e. g., methyl sulphate, ethyl sulphate, etc. The desired compounds separate from the aqueous solutions. It is to be understood that it is the product (or products) of this reaction which are contemplated by Formula I above wherein R is an alkyl group.

The results in the above table show that the compounds of our invention are not only useful as antifoggants, but that they also stabilize photographic emulsions against loss in speed in many instances.

In a manner similar to that illustrated in the above example, other aminothiazoles selected from those represented by the above general Formula I can be incorporated in photographic emulsions for the purpose of stabilization. The fog-inhibiting agents useful in practicing our invention can be used in various kinds of photographic emulsions. In addition to being useful in ordinary non-sensitized emulsions, they can also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they can be added to the emulsion before or after the dyes are added. Suitable dispersing agents for the silver halide emulsions stabilizec' according to our invention comprise gelatin, or othei as collodion, albumen, cellulose organic derivatives, synthetic resins, etc.

a'given eniulsion will vary depending on the resence of emulsion addenda, such as che'micalsensitizers, optical sensitizers, era: In general, w have foundthat from 0.001 to 5.0 goof fog-inhibiting agent'p er mole of silver halide is sufilcient for the purposes of our invention.

Instead of adding,thefog inhibiting agent directly to the photographic emulsion, it is sometimes desirable to incorporate thefog-inhibiting agent in a separate layer which is placed in contact with the silver halide emulsion layer which is to be stabilized. Under such conditions, of course, it is advisable to use a higher concentration of fog-inhibiting agent than indicated above.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion containing a compound selected from those represented by the following general formula:

emulsion making. Of course, the optimum amount for wherein R represents a member selected from the group consisting of an alkoxyl group and an amino group, and R represents a member selected from the group consisting of a hydrogen atom and a lower alkyl group.

2. A photographic gelatino-silver-halide developingout emulsion containing a compound selected from those represented by the following general formula Elf-i l L-SH wherein R represents a member selected from the group consisting of an alkoxyl group and an amino group, and R represents a member selected from the group consisting of a hydrogen atom and a lower alkyl group.

4. A photographic gelatino-silver-halide developing- 1 outemulsion containing a compound selected from those represented by the following general formula:

wherein R represents a member selectedfrom the group consisting of an ethoxyl group and ari amino'group and R represents .a member selected from the group consisting of a hydrogen atornand a methyl group.

5. A photographic gelatino'silver bromiodide developf ing-out emulsion containing a compound selected from those represented by the following general formula:

6. A photographic silver halide emulsion containing a compound. represented by the following formula:

7. .A photographic silver halide emulsion containing a represented by thefollowing formula;

M V a V CE; S 8. A photographic silver halide emulsion containing a compound represented by the following formula:

9. A photographic silver halide emulsion containing a compound represented by the following formula:

References Cited in the file of this patent UNITED STATES PATENTS 2,453,346 Russell Nov -9, 1948 FOREIGN PATENTS 124,625 Australia June 17, 1947 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COMPOUND SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 